1. Field of the Invention
The present invention relates to a self-advancing type photographic film cassette and more particularly to improvements to light-trapping members to be attached to a film passage mouth.
2. Description of the Related Art
A conventional 135 type (35 mm) photographic film cassette is disclosed by Japanese Utility Model Publication No. 61-34526. Such a photographic film cassette has plush attached to a film passage mouth or a film passageway as light-trapping members so as to prevent ambient light from entering the film passage mouth. Recently, it is known to utilize a film cassette in which a leading end of a photographic film is advanced or propelled to an outside of a cassette shell by rotating a spool in a film unwinding direction. In such photographic film cassettes, it is necessary to reduce friction between the photographic film and the light-trapping members in order to propel the leading end smoothly through the film passage mouth out of the cassette shell with a small torque. For this purpose, various materials for the light-trapping members have been proposed in place of the conventional plush. For example, in a photographic film cassette disclosed in U.S. Pat. No. 3,537,376, light-trapping members comprise a flexible or compressible layer such as polyurethane and a facing layer having low coefficients of friction against the photographic film.
A leading end of the photographic film in the photographic film cassette shell disclosed in U.S. Pat. No. 3,537,376 is initially extended slightly to the outside of the cassette shell through the film passage mouth, and thus the construction of the photographic film cassette therein is not adaptable to the type of film cassettes in which the entire length of photographic film is initially contained in the cassette shell and its leading end is advanced out of the cassette shell by rotation of the spool. For example, the innermost portions of the light-trapping members are not adhered to the inside surfaces of the film passage mouth. Therefore, even if the spool were rotated so that the photographic film, including its leading end, were advanced out of the cassette shell, the leading end would be caught by the innermost ends of the light-trapping members making it impossible to advance the film out of the cassette shell. Further, the surfaces of the light-trapping members are easily damaged by creases and irregularities formed during manufacture. This causes a reduction in their light-trapping ability.
As the speed of photographic films has been highly improved recently, a high light-trapping ability of light-trapping members is required. However, when the above-mentioned flexible layer is pressed for a long time or heated, its flexibility decreases so as to deteriorate the light-trapping ability thereof. A facing layer is generally adhered to the flexible layer by a flame-laminating process in which the facing layer is attached to a heat-melted surface of the flexible layer. But, this flame-laminating method reduces the thickness of the completed light-trapping members, resulting in fogging of the photographic film. If the film passage mouth were made narrower or the thickness of the light-trapping members were made longer, as countermeasures for this, the required advancing torque would be increased.